Today’s earthquake was strongly felt in Jackson, WY. It is a strike-slip event with the center of the rupture at a depth of about 14 km (9 mi). It struck in a region that has been seismically active for the past 20 years, with a seismicity alignment that hints at a blind right-lateral fault striking NW-SE, which would be consistent with the focal mechanism of today’s quake.

The 26 February 2016 M=4.0 quake lies in a region of low hazard—about one-eighth of that in the southern San Francisco Bay area, but still much larger than about 85% of the United States, and close to the beautiful Teton fault, which lifted up the Grand Tetons, and formed the meadows and Jenny Lake on its downthrown side.Google Earth view of the Teton Fault that has lifted up the Grand Tetons, one of the greatest of the US National Parks. The photo is about 35 mi (60 km) wide and North is to the right.

The Teton fault is the product of Basin & Range stretching, creating ‘normal’ (tensional) faults. Its spectacular post-glacial scarps are present along the entirefault trace, and can be seen from the valley floor owing to their large height. The post-glacial (meaning, less than 15,000 year old) fault offset is as much as 100 ft (30 m) along the middle part of the range, but diminishes to the north and south, mimicking the overall height of the Teton ranges. Although quite active in the latest Quaternary, the fault has been seismically quiet in historic time. Its estimated slip rate is 1-5 mm/yr.

Today’s quake struck within a nest of seismicity that has persisted for the past 20 years—near but definitely not on the Teton fault. Source: USGSOne of the most exciting uses of Temblor is to open it in the field, so you can see exactly where the fault scarps have been etched into the landscape. This photo was taken by Temblor developer, Ali Kim, on a backpacking trip last summer. I backpacked into the high country with my daughter there four years ago, where we had a sudden but fortunately safe encounter with a black bear.